Sequence and functional characterization of the terminal exon of the human insulin receptor gene

We present 5.1 kb of the 3' noncoding region sequence of the human insulin receptor gene and identification of four functional polyadenylation domains responsible for 3'-end processing of the 5.4, 6.9, 8.0 and 9.4 kb human insulin receptor mRNA, respectively. The insulin receptor gene contains five putative polyadenylation sites (P1-P5), located 5160, 6502, 7488, 8945 and 8957 base pairs (bp) downstream from the translational initiation site. All putative polyadenylation sites are flanked by upstream AU rich and downstream GU rich regions which regulate mRNA stability and mRNA cleavage, respectively. Also, two RNA stem-loop structures have been identified. To determine its role on gene expression, a reporter gene was constructed containing various lengths of the insulin receptor 3' UTR and transiently transfected into COS 7 cells. A 539 bp fragment (4897-5436 bp downstream from the IR translational initiation site) inhibited CAT expression by 5-6 fold. Further downstream addition of 1169 bp of the insulin receptor 3' untranslated region enhanced gene expression by 2-fold. These studies provide evidence that the insulin receptor 3' untranslated region can modulate gene expression.